opengl - Sphere Tessellation wrong coordinates -

i'm trying apply tessellation on gpu simple sphere. tessellation working simple plan, it's not working sphere. of course, know coordinates mapping aren't same, tried many ways it. example, tried use gl_tesscoord (x , y) in tessellation evaluation longitude et latitude mapped plane. convert them spherical coordinates, 'really' didn't work.

for tessellation control, i'm splitting patches 2 outer , 2 inner level.

here code draw sphere :

glbindvertexarray(vertexarrayobject); glpatchparameteri(gl_patch_vertices, 4);   glbindbuffer(gl_element_array_buffer, indicesbuffer); gldrawelements(gl_patches, indices.length, gl_unsigned_int, 0);   glbindvertexarray(0); 

here current code in tessellation evaluation :

#version 430    layout(quads, fractional_even_spacing, ccw) in;   uniform mat4 u_projectionmatrix;  uniform mat4 u_viewmatrix;  uniform mat4 u_transformmatrix; uniform float u_radius;   uniform vec3 u_cameraposition;      void main(void){ vec4 position = gl_in[0].gl_position; position.xz += gl_tesscoord.xy * 2.0 - 1.0;  gl_position = u_projectionmatrix * u_viewmatrix * u_transformmatrix * position;  } 

here indices :

int indptr = 0;

for(int r=0; r< mrings-1; r++) for(int s=0; s<msectors-1; s++){ indices[indptr++] = r * msectors + s;  indices[indptr++] = r * msectors + (s+1);  indices[indptr++] = (r+1) * msectors + (s+1);  indices[indptr++] = (r+1) * msectors + s;  } 

to draw sphere, followed example : creating 3d sphere in opengl using visual c++ credits go him (and thank way !).

here 2 images showing result :

if have hint me solve problem, it'd cool. thank you. note : if need other informations, please ask me , i'll post them.

seems you're taking first vertex (which lies on sphere) , offset horizontally (on xz plane) gl_tesscoord.xy:

vec4 position = gl_in[0].gl_position; position.xz += gl_tesscoord.xy * 2.0 - 1.0;  

since you're producing quads, take gl_in of size 4 points. you're interrested in first three. final position can interpolated this:

vec4 = mix(gl_in[1].gl_position, gl_in[0].gl_position, gl_tesscoord.x); vec4 b = mix(gl_in[2].gl_position, gl_in[3].gl_position, gl_tesscoord.x); gl_position = projectionmatrix * viewmatrix * transformmatrix * mix(a, b, gl_tesscoord.y); 

(source)

that should fix problem.

p.s. normals, following (if sphere generated around origin):

vec3 normal = mat3x3(viewmatrix*transformmatrix) * normalize(position.xyz);